Device for separating recording medium for use in electrophotographic copying machines

ABSTRACT

A separating device for an electrophotographic copying machine consisting of a stationary or running belt and guide members for the belt. The belt extends through the nip between the photosensitive drum and the transfer roller of the copying machine. After the recording medium passes between the drum and the transfer roller, the medium is separated from the drum by the belt and subsequently separated from the belt by at least one of the guide members.

United States Patent Ito et al.

DEVICE FOR SEPARATING RECORDING MEDIUM FOR USE IN ELECTROPHOTOGRAPHICCOPYING MACHINES Inventors: Yoshio Katayama, Kawasaki; Masaru Yamaguchi;Hiroshi Nitanda, both of Tokyo, all of Japan Assignee: Canon KabushikiKaisha, Tokyo,

Japan Filed: Aug. 26, 1970 Appl. No.: 67,049

Foreign Application Priority Data Aug. 30, 1969 Japan ..44/68790 Dec.12, 1969 Japan ..44/l002l7 Dec. 12, 1969 Japan ..44/26l62 US. Cl..355/3, 271/DIG. 2 Int. Cl. ..G03g 15/14 Field of Search ..355/3, 10,12, l5, 16, 104, 355/106, 117; 27l/DlG. 2

Ito, Tokyo; Haiini'e 51 Aug. 15, 1972 [56] References Cited UNITEDSTATES PATENTS- 3,450,402 6/1969 Weiler ..27l/DlG. 2 3,386,730 6/1968Hyosaka ..355/1 10 X 3,139,013 6/1964 Graves ..355/3 3,506,259 4/1970Caldwell et al. ..355/3 X Primary Examiner-Samuel S. Matthews AssistantExaminer-Fred L. Braun AttorneyWard, McElhannon, Brooks & Fitzpatrick [57] ABSTRACT A separating device for an electrophotographic copyingmachine consisting of a stationary or running belt and guide members forthe belt. The belt extends through the nip between the photosensitivedrum and the transfer roller of the copying machine. After the recordingmedium passes between the drum and the transfer roller, the medium isseparated from the drum by the belt and subsequently separated from thebelt by at least one of the guide members.

8 Claims, 7 Drawing Figures DEVICE FOR SEPARATING RECORDING MEDIUM FORUSE IN ELECTROPHOTOGRAPIIIC COPYING MACHINES BACKGROUND OF THEINVENTION 1. Field of Invention The present invention relates to a noveldevice for separating a recording medium electrostatically attached toan electrophotographic photosensitive member of an electrophotographiccopying machine.

2. Description of Prior Art In general, an electrophotographic copyingmachine comprises a rotary drum having a photosensitive layer which ischarged and exposed with a light image, the electrostatic image beingdeveloped and transferred to a recording medium. In the image transferstep, the recording medium must be pressed against the photosensitivedrum, but after the image transfer, it must be separated from the drum,which is cleaned for the next copying step. Because the recording mediumis in general a paper, it tends to be electrostatically attached to thedrum so that it is not separated with ease. Therefore, a suitable devicefor separating the recording medium from the drum after image transfermust be provided.

There have been proposed various means for separating the recordingmedium from the photosensitive drum. For example, one device utilizesvacuum to suck the recording medium away from the photosensitive drum.In another device, air under high pressure is blown against the leadingedge of the recording medium along the peripheral surface of thephotosensitive drum. However, both of the separating devices mustoperate in synchronism with the transport of the recording medium.Furthermore, both of the devices employ compressors or pumps so thatthey are expensive and the problem of noise occurs. In the latterdevice, the toner is blown by the air from the blower into the machineso that the components are contaminated.

SUMMARY OF THE INVENTION It is therefore one of the objects of thepresent invention to provide a device for separating from aphotosensitive drum a recording medium which eliminates the defectsdescribed above and is economical and simple in construction.

It is another object of the present invention to provide a device forseparating a recording medium from a photosensitive drum in which arecording medium separating member is held stationary so that thedriving means and synchronizing means are not required, and whosefunction is positive and reliable.

It is another object of the present invention to provide a device forseparating a recording medium from a photosensitive drum in which aseparating member in the form of an endless belt rotates together with aseparating roller so that no driving means and synchronizing means arerequired. The separating device always has a function of separating arecording medium from a photosensitive drum so that the recording mediummay be always positively separated.

In brief, the present invention is characterized in that in anelectrophotographic copying machine comprising a rotary drum having aphotosensitive layer, charging means, exposure means, developing means,image present invention;

transfer means and cleaning means arranged around the photosensitivedrum, a recording medium is so guided by a separating belt as to bemoved away from the photosensitive drum.

BRIEF DESCRIPTION OF THE DRAWING FIG. .I is a perspective viewillustrating an electrophotographic copying machine to which is appliedFIG. 2 is a diagrammatic front view thereof illustrating the majorcomponent members;

FIG. 3 is a side view on enlarged scale illustrating a first embodimentof the present.invention;

FIG. 4 is a perspective view thereof;

FIG. 5 is a side view on enlarged scale illustrating a second embodimentof the present invention;

FIG. 6 is a side view illustrating a third embodiment of the presentinvention; and

FIG. 7 is a fragmentary front view thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENT Various component members of anelectrophotographic copying machine embodying the present invention areshown in FIG. 2. Around a photosensitive drum 1 having a photosensitivelayer 2 are disposed a charger 4, an exposure station 5, a developingstation 7, an image transfer station 9 and a cleaning station 10 in theorder named in the direction of rotation of the drum 1 as shown by thearrow.

A separatingdevice in accordance with the present invention isillustrated in FIG. 3 together with the major component members in theimage transfer station. A recording medium to which is transferred atoner image formed upon the drum 1 is fed between a transfer roller 13and the drum 1 through a pair of feed rollers 28 and a pair of guides29in the direction indicated by the tangent AA passing through the pointof contact between the transfer roller 13 and drum 1.

The transfer roller 13 whose axis is substantially in parallel with thatof the drum 1 is made of a resilient electric conductor having a lengthslightly longer than that of the width of the largest copy reproduced bythe electrophotographic copying machine. The transfer roller 13 ispressed against the drum 1 by means of a spring or the like andelectrically biased if required. When the toner image upon the drum 1 istransferred to the recording medium P, the latter is electrostaticallyattracted toward the drum 1 so that the device for separating therecording medium P from the drum 1 must be provided.

For this purpose, a separating belt 14 is extended from the front of theroller 13 along the tangent AA and wrapped around a driven roller 18, adrive roller 16, a tension roller 17 and a separating roller 15. Theseparating roller 15 rotates at a peripheral speed V equal to orslightly faster than the peripheral speed v of the drum 1 and is adaptedto move the separating belt 14 away from the drum 1 since the belt 14 iswrapped around the arc of the separating roller 15 subtended by acentral angle ofa (between 0 and That is, the recording medium P istransported in such a manner that one side edge of the recording mediumP may be separated from the drum 1 during the time the toner image isbeing transferred from the drum 1 to the recording medium P. Afterpassing over the transfer medium P. The width of the transfer roller 13may be reduced by the width of the separating belt 14 in order toeliminate the friction between them and the wrinkles of the recordingmedium P. The width of the drum 1 must be wider than that of therecording medium because when the former is shorter than the latter, therecording medium is stained by the side edges of the drum 1.

The separating belt 14 is normally under tension by means of the tensionroller 17 which is loaded with a spring 30. The separating belt 14 whichis transported in the direction indicated by the arrow at a speedsubstantially equal to that of the recording medium makes frictionalcontact with the drum 1 so that the separating belt 14 may be preferablymade of a material having a small coefficient of friction such as Myler,Teflon' (Trade Name) interwoven with glass fibers. Preferably thethickness is 50 to 15 p. and the width is to 20 In order to preventslippage between the separating belt 14 and the drive roller 16, thelatter is preferably made of a material having a greater coefficient offriction. For example, the drive roller may be covered with rubber. Therecording medium P discharged from the image transfer station istransported into the fixing station by means of a guide 21 between abelt 12 and the separating roller 15. The function of a blower 31 forblowing weak air upon the recording medium P may be described in moredetail hereinafter.

As explained above, the recording medium P contacts the drum 1 duringthe time the toner image formed upon it is being transferred to therecording mediumP which is transported into the nip between the drum 1and the transfer roller 13 by means of the feed rollers 28 and theguides 29, but the side edge portion of the recording medium P isinterposed between the separating belt 14 and roller 15 so as to bemoved away from the drum 1 immediately after passing over the transferroller 13. Therefore, the recording medium P may be gradually separatedfrom the drum 1 from the side edge portion around the separating roller15 with the contact angle or toward the opposite side edge.

The contact angle a between the belt 14 and the roller 15 should betterbe increased and the position of the separating roller 15 shouldpreferably be nearer to the transfer roller 13 to improve the separationfunction. When the recording medium P is separated from the drum 1, itlies on the guide 21 and by the frictional force between the driveroller 16 and the guide 21 the medium P is fed to the belt 12'. In orderto facilitate the separation of the recording medium P from the drum 1by means of the separating belt 14 and roller 15, the present inventionfurther provides the blower 31 so as to blow weak air upon the recordingmedium P separated from the drum 1 in the direction of the wedge-shapedspace between the drive roller 16 and the recording medium P. Thereforethe air from the blower 31 not only serves to separate the recordingmedium P from the drive roller 16 but also presses the recording mediumagainst the guide 21 and the belt 12' so as to securely transport therecording medium into the fixing station. I

-The advantages of the above explained invention are as follows:

1. Since the recording medium separating device is always in operation,the recording medium can be positively and securely separated from thephotosensitive drum; I

2-. Since the recording medium separating device is not required to beoperated in synchronism with the transportation of a recording medium,the

. device becomes simple in construction and relatively low in cost;

3. Since the endless separating belt is always driven while theseparating roller is rotated, there is no friction between theseparating roller and belt so that wear of separating belt may beminimized;

4. The endless separating belt is always in contact with the separatingroller under tension, so that the recording medium interposedtherebetween may be always positively separated from the photosensitivedrum in a stabilized manner;

5. The endless separating belt may be arranged within the width of thephotosensitive drum so that it may not extend beyond the side edge ofthe drum; and

6. Since the width of the photosensitive drum may be made greater thanthat of the recording medium, the latter may be prevented from beingstained by the edges of the drum. It is seen that the present inventionmay be also applied to -a -plate-shaped photosensitive member.

Next referring to FIG. 5, the second embodiment of the present inventionwill be described, but the description is limited to those featuresdifferent from the first embodiment. Opposed to the first embodiment.the separating belt 14 in the second embodiment is stationary. One endof the separating belt 14 is fixed to a pin 18' while the other end isfixed to a hook-like member 33 which in turn is fixed to a spring 30 soas to impart a suitable tension to the separating belt 14. Aguideroller32 is provided for bending the separating belt 14 as shown.As in case of the first'embodiment, the separating belt is preferablymade of a material having a smaller coefficient of friction.

The toner image is transferred from the drum 1 to the recording medium Pwhich is fed through the feed rollers 28 and the guides 29 into the nipbetween the drum '1 and the transfer roller 13 which presses therecording medium against the drum 1. In this case, the recording mediumP is transported along the undersurface of the separating roller 13toward the separating roller 15 which is rotating at the speed V atleast as fast as or faster than the peripheral speed v of the drum 1 asin the case of the first embodiment. Furthermore, the separating belt 14is wrapped around the arc of the separating roller 15 subtended by thecentral angle a as in the case of the first embodiment. In consequence,the tension is applied to the recording medium P between the transferand separating rollers 13 and 15 and is moved away from the drum 1 alongthe separating roller 15. Thus, the side edge portion of the recordingmedium is separated from the drum 1 immediately passing over thetransfer roller 13 so that as the recording medium is transported, itmay beseparated gradually from its side edge on the side of theseparating belt toward its opposing side edge. The greater the angle ofcontact a between the separating belt and roller 14 and 15 and thenearer the separating roller 15 is located toward the transfer roller13, the more the separation may be facilitated. Furthermore, the greaterthe peripheral speed V of the separating roller 15 than the peripheralspeed v of the drum 1, the greater the tension applied to the recordingmedium between the transfer and separating rollers 13 and 15 so that theseparation of the recording medium P from the drum 1 may be facilitated.The recording medium P emerging from the separating roller 15 is droppedupon the guide 21 and is advanced toward the belt 12. The secondembodiment is also provided with the blower 31 and may be applied to anelectrophotographic copying machine employing a plate-likephotosensitive member. The other modification is characterized in thatthe diameter of one or both side edge portions of the transfer roller isreduced to such an extent that they will not make contact with thephotosensitive drum through the recording medium and the separating beltand the reduceddiameter-side-edge-portion or portions rotates togetherwith the transfer roller so that the recording medium may be so guidedby the separating belt as to be moved away from the drum. Alternatively,the reduced-diameter-side-edge-portion or portions may be heldstationary. Other arrangements are similar to those of the first andsecond embodiments. The third embodiment will be described withreference to FIGS. 6 and 7. Opposed to the first and second embodiment,the third embodiment eliminates the separating roller, but the transferroller also serves as a separating roller. A transfer roller 113 made ofan electrically conductive rubber is always pressed against thephotosensitive drum 1 under the force of a spring, not shown, and isrotated as the drum 1 rotates. Since the recording medium P iselectrostatically attracted by the drum 1, it tends it be transportedtogether with the drum 1. A ring 114 made of a metal for guiding therecording medium P is coaxially carried by the shaft of the transferroller 113, but is prevented from rotating by a pin 120 fitted into anotch 120' of the guide ring 114. In order to prevent the ring 114 fromcausing the damage to drum 1 because the recording medium is deformeddue to the contact of the transfer roller with the drum 1, the ring isprovided with a cut-away portion A.

One end ofa wear resistant belt 115 having a smooth surface made of forexample a fluoro-resin film is fixed to a pin 118 located forwardly ofthe transfer roller 113, and the other end is joined to the belt 115 atB after it is wrapped around the pins 116 and 1 17 and the drum 1. Thus,the separating device is constituted by the ring 114 and the belt 115.The device is preferably provided along one side edge of the drum 1, butif required, the devices may be provided along both side edges of thedrum 1. Furthermore, the belt 115 may be an endless belt wrapped aroundthe pins 116, 117 and 1 18.

When the recording medium P is fed into the nip between the drum 1 andthe transfer roller 113 from the guide 119, the side edge portion of therecording medium P is interposed between the belt 115 and the ring 114.Preferably, the joint B is so selected that a suitable gap may be formedbetween the belt and the ring 114, whereby the recording medium fed intothe nip between the drum 1 and the ring 114 may not be stopped. Sincethe side edge portion, which is generally 10 mm in width, is sandwichedbetween the belt 115 and the ring 114, the side edge portion ofrecording medium may be forced to be separated from the drum 1 as it isadvanced along the drum so that the recording medium is graduallyseparated from the drum 1 as soon as the image transfer is completed. Nowrinkles are formed because the recording medium is transported betweenthe belt 115 and the ring 114. The recording medium wrapped around thetransfer roller 113 or the ring 114 may be separated by a separatorguide 121 and transported toward the fixing station.

What is claimed is:

1. In an electrophotographic copying machine including a housing, aphotosensitive drum in said housing, charging means, exposure means,developing means, image transfer means having a transfer roller adjacentthe drum, and recording medium separating means arranged around saidphotosensitive drum; the recording medium separating means comprising, aseparating belt extending through the nip between said photosensitivedrum and said transfer roller and adapted to contact at least one endportion of said recording medium, means for guiding said separating beltand for separating the recording medium from the separating belt aftersaid medium has been separated from the photosensitive drum, and meansfor transporting the recording medium so as to press it against saidphotosensitive drum through said separating belt.

2. The copying machine according to claim 1. wherein said separatingbelt is an endless belt, and said guide means comprise a separatingroller disposed immediately after said transfer roller and out ofcontact with said photosensitive drum when the recording medium and saidseparating belt pass therebetween, a drive roller disposed in a positionfor redirecting the recording medium passed over said separating rollerin a direction away from said photosensitive drum, and a guide rollerfor imparting tension to said separating belt.

3. The copying machine according to claim 2, wherein said separatingroller rotates at a peripheral speed substantially equal to or fasterthan that of said photosensitive drum.

4. The copying machine according to claim 2, wherein blower means isprovided for blowing air against the recording medium separated fromsaid photosensitive drum by said separating belt.

5. The copying machine according to claim 2, wherein said drive rolleris disposed in a position for directing the separated recording mediumin a direction away from the photosensitive drum and keeping a contactangle of less than between said drive roller and the recording medium.

6. The copying machine according to claim 1, wherein the side edgeportion of said transfer roller has a diameter smaller than that ofthemajor portion of said transfer roller whereby said side edge portionof said transfer roller is out of contact with said photosensitive drumeven when said separating belt and the recording medium passtherebetween.

8. The copying .machine according to claim 1,

wherein said guide means comprises pins to which are securely fixed theleading and the trailing ends of said separating belt, and guide pinsfor moving the recording medium away from said photosensitive drum afterimage-transfer. I

1. In an electrophotographic copying machine including a housing, aphotosensitive drum in said housing, charging means, exposure means,developing means, image transfer means having a transfer roller adjacentthe drum, and recording medium separating means arranged around saidphotosensitive drum; the recording medium separating means comprising, aseparating belt extending through the nip between said photosensitivedrum and said transfer roller and adapted to contact at least one endportion of said recording medium, means for guiding said separating beltand for separating the recording medium from the separating belt aftersaid medium has been separated from the photosensitive drum, and meansfor transporting the recording medium so as to press it against saidphotosensitive drum through said separating belt.
 2. The copying machineaccording to claim 1, wherein said separating belt is an endless belt,and said guide means comprise a separating roller disposed immediatelyafter said transfer roller and out of contact with said photosensitivedrum when the recording medium and said separating belt passtherebetween, a drive roller disposed in a position for redirecting therecording medium passed over said separating roller in a direction awayfrom said photosensitive drum, and a guide roller for imparting tensionto said separating belt.
 3. The copying machine according to claim 2,wherein said separating roller rotates at a peripheral speedsubstantially equal to or faster than that of said photosensitive drum.4. The copying machine according to claim 2, wherein bLower means isprovided for blowing air against the recording medium separated fromsaid photosensitive drum by said separating belt.
 5. The copying machineaccording to claim 2, wherein said drive roller is disposed in aposition for directing the separated recording medium in a directionaway from the photosensitive drum and keeping a contact angle of lessthan 180* between said drive roller and the recording medium.
 6. Thecopying machine according to claim 1, wherein the side edge portion ofsaid transfer roller has a diameter smaller than that of the majorportion of said transfer roller whereby said side edge portion of saidtransfer roller is out of contact with said photosensitive drum evenwhen said separating belt and the recording medium pass therebetween. 7.The copying machine according to claim 6, wherein a stationary ring isloosely fitted near to the side edge of said transfer roller, thediameter of said ring being selected in order that said ring is out ofcontact with said photosensitive drum even when the recording medium andsaid separating belt pass therebetween.
 8. The copying machine accordingto claim 1, wherein said guide means comprises pins to which aresecurely fixed the leading and the trailing ends of said separatingbelt, and guide pins for moving the recording medium away from saidphotosensitive drum after image-transfer.